1. Field of the Invention
The present invention relates to a magnetic head for use in a magnetic disk drive, and more specifically, to a magnetic head for use for writing data on a recording medium by means of a perpendicular magnetic recording system.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
In each of the longitudinal magnetic recording system and the perpendicular magnetic recording system, magnetic heads typically used have a structure in which a read head having a magnetoresistive element (hereinafter also referred to an MR element) for reading and a write head having an induction-type electromagnetic transducer for writing are stacked on a substrate.
In each of the longitudinal magnetic recording system and the perpendicular magnetic recording system, the write head includes a coil for generating a magnetic field corresponding to data to be written on the recording medium, and a pole layer for allowing a magnetic flux corresponding to the magnetic field generated by the coil to pass and for generating a write magnetic field for writing the data on the recording medium.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has a medium facing surface that faces toward the recording medium. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider.
To improve the recording density and the signal-to-noise ratio, a reduction in flying height of the slider is required. For example, it is expected that a reduction in flying height of the slider to 2 nm or smaller will be required to achieve an areal recording density of 400 Gbpsi or greater. However, a reduction in flying height of the slider causes the slider to more easily collide with the recording medium, and thus increases the possibility of damage to the recording medium and the magnetic head.
In addition, there is a problem that in a magnetic head, heat generated by the coil during operation causes expansion of a coil insulating layer disposed around the coil, thereby causing protrusion of part of the medium facing surface. If the amount of protrusion of the part of the medium facing surface is great, the slider becomes more likely to collide with the recording medium, and therefore it becomes difficult to reduce the flying height of the slider. This makes it difficult to improve the recording density and the signal-to-noise ratio.
Typically, a resist is often used as the material of the coil insulating layer. Resists are greater in thermal expansion coefficient than alumina (Al2O3), which is often used as an insulating material in a magnetic head. In a magnetic head in which a resist is used as the material of the coil insulating layer, it is therefore difficult to suppress the protrusion of part of the medium facing surface induced by the heat generated by the coil.
U.S. Patent Application Publication No. US 2007/0064344 A1 discloses a magnetic head in which SiO2, Si nitride or Si oxide having a low thermal expansion coefficient is used as the material of the coil insulating layer. In this magnetic head, however, it is difficult to dissipate heat generated by the coil during operation, because SiO2, Si nitride and Si oxide are low in thermal conductivity. Consequently, in this magnetic head, the temperature of the coil greatly increases during operation, so that it becomes difficult to suppress the protrusion of part of the medium facing surface induced by the heat generated by the coil.